Image reading apparatus and image reading method

ABSTRACT

An image reading apparatus for reading indicia on the front and back surfaces of a document using two image sensors includes a document detection sensor to detect the document, a first image sensor for reading an image on one surface of the document, a second image sensor for reading an image on the other surface of the document, and a controller. The controller starts to read the image data from the first and second image sensors when prescribed amounts of time have passed after the document detection sensor detects the leading edge of the document, and stops the reading of the image data from the image sensors. The structure provides a lightweight and compact apparatus while reducing image noise caused by the mutual interferences of the light sources in reading the image data.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

[0001] This invention relates to an image reading apparatus and imagereading method for scanning and optically reading a document image andoutputting the electronic data. More particularly, this inventionrelates to an image reading apparatus equipped with two optical readingsensors for reading the images on the upper and lower surfaces of adocument or sheet fed one by one from a document reception tray by anautomatic document feeder commonly known as an ADF.

[0002] Image reading apparatuses, normally called scanners, opticallyread the image of a document and convert the image into electronic dataand transmit it to image forming apparatuses, such as personalcomputers, copy machines or facsimiles. Image forming apparatuses arealso normally equipped with the following types of image readingapparatuses.

[0003] The image reading apparatuses have image sensors for reading theimages on a document or sheet transferred one by one from a documentreception tray by an automatic document feeder. Furthermore, recentimage reading apparatuses have been proposed to have functions to readthe images on the upper and lower surfaces of a document or sheet fedone by one by the automatic document feeder on one document transportpath without transferring to a switch-back pass, by using two individualimage sensors.

[0004] Examples of the image reading apparatuses that are equipped withtwo image sensors to read the images on the upper and lower surfaces ofa document are Japanese Patent Publications (KOKAI) No. 62-258552(hereinafter referred to as prior art 1), and No. 10-145538 (hereinafterreferred to as prior art 2).

[0005] The image reading apparatus as disclosed in prior art 1 discloseslighting apparatuses for both upper surface and lower surface of adocument or sheet, and an optical system that employs CCD and a linesensor to simultaneously read indicia on both surfaces of the document.

[0006] Also, in the facsimile apparatus disclosed in the prior art 2, asshown in FIG. 15 (FIG. 2 and FIG. 5 of the same publication), a lineimage sensor 123 for reading the indicia on the upper surface of adocument starts to read the image data on the upper surface based on thedetection of the leading edge of the document by a document sensor 122,and a line image sensor 124 for reading the images on the bottom surfaceof the document starts to read the image data thereof. Also, because theline image sensor 124 is located at a position away from the line imagesensor 123 for a distance of only L2, if both line image sensors aredriven at the same time, the image signals on both surfaces offset theline count equivalent to the distance of L2. Thus, by always monitoringthe offset line count, transport errors of the document is determined.

[0007] Also, as an image sensor reading operation controller, it employsthe output signals from the image sensor and a clock for synchronizationas well as a drive controller to stop reading, as the method to controlthe reading operation.

[0008] In order to form a lighter weight and more compact image readingapparatus for reading the image data on both surfaces of documents orsheets, it is essential to locate a reading position for reading theimages on one surface of a document (upper surface) and a readingposition for reading the images on the other surface of a document(lower surface) as close as possible without a large gap therebetween.If the upper surface reading position and the lower surface readingposition are disclosed close to each other, there is increased a dangerof the light from the light source device for illuminating one surfaceof the document passing through the document sheet and being detected bythe image sensor on the other surface, so that the mutual interferencesof the upper and lower light sources cause electronic noise in the imagedata read from both surfaces.

[0009] However, in the prior art 1, both the line sensor for reading theupper surface of the document and the line sensor for reading the lowersurface of the document use optical system (optical reduction typeemploying CCD) line sensors. Therefore, if the reading position for theone or upper surface of the document and the reading position for theother or lower surface of the document are arranged in the sameposition, the apparatus will become more compact and lightweight, butimage data read from both surfaces will cause noise to be generated.

[0010] Also, in the prior art 2, the first line sensor for reading theindicia on the upper surface of the document starts to read the imagedata from the upper surface of the document based upon the detection ofthe leading edge of the document by the document sensor, and the secondline sensor for reading the indicia on the lower surface of the documentoperates simultaneously with the detection by the document sensor. Insuch case, if monitoring the line count offset according to the distanceLD for the image signal of both surfaces, an unnecessary amount of imagedata is recorded, requiring the entire controller device to be morecomplex, thus making it impossible to lighten the weight of theapparatus and to make the overall apparatus more compact. Furthermore,in the prior art 2, as in the prior art 1, there is no disclosureregarding the reduction of the image noise that occurs by the mutualinterferences of the upper and lower light sources in reading the imagedata from both surfaces.

[0011] Thus, an object of the present invention is to provide a documentreading apparatus to read indicia on both surfaces of a document orsheet using two image sensors, which is light in weight and morecompact, and has a small distance of the gap between a first imagesensor and a second image sensor to reduce the image noise caused by themutual interferences of the upper and lower light sources as little aspossible.

[0012] Another object of the present invention is to provide a documentreading apparatus to read the indicia on both surfaces of the documentusing two image sensors, wherein a controller for reading images issimplified to reduce the weight and to make the apparatus more compact.

[0013] Further objects and advantages of the invention will be apparentfrom the following description of the invention.

SUMMARY OF THE INVENTION

[0014] The image reading apparatus is directed to read indicia on theupper surface and the lower surface of a document or sheet transferredby an automatic document feeder for feeding one sheet at a time. Thedocuments or sheets are stacked on a document supply tray. The apparatusincludes a document detection sensor to detect the document transportedfrom the document supply tray, a first image sensor for reading theimages on one surface of the document, a second image sensor for readingthe images on the other surface of the document, and a controllerdevice. The controller device starts reading from each of the firstimage sensor and the second image sensor at the point when prescribedamounts of time have passed after the document detection sensor detectsthe leading edge of the document.

[0015] Furthermore, the apparatus may includes a document sensor fordetecting the document transported from the document supply tray, afirst image sensor for reading the images on one surface of thedocument, a second image sensor for reading the images on the othersurface of the document, and a controller device. The controller devicestops the reading from each of the first image sensor and the secondimage sensor at the point when prescribed amounts of time have passedafter the document detection sensor detects a trailing edge of thedocument. This simplifies the timing control for starting the reading ofthe image data in the present invention.

[0016] The first light source included in the first image sensor and thesecond light source included in the second image sensor are controlledso that each is lit just prior to start the reading of the image data oneach surface of the document and each is extinguished just after readingthe image data. Also, while simultaneously taking or reading the imagedata from the first image sensor and the second image sensor, thequantity of light from at least one of the first image sensor and thesecond image sensor is controlled, so that the mutual interferences oflight radiating from the upper and lower light sources are minimized andthe generation of noise in the image data read from both surfaces of thedocument is reduced as little as possible.

[0017] Here, the first image sensor is composed of an optical reductionreading sensor and the second image sensor is composed of a contactimage sensor.

[0018] In addition, a straight transport path is formed along at leastthe first image sensor and the second image sensor throughout thedocument sheet path, to eliminate slippage of any rollers on thedocument and to allow the smooth travel of the document thereby enablingthe accurate reading of the images on both of the upper and lowersurfaces thereof.

[0019] This invention substantially simultaneously takes the image datafrom both the upper and lower surfaces of the document using twoindividual image sensors, so that the controller means of this apparatusconverts the image data taken by the first image sensor and the secondimage sensor from analog signals to digital signals, and is equippedwith memory means to temporarily store that data in the duplex readingmode. It reciprocally outputs the image data from the image line of onesurface of the document taken by the first image sensor and the imagedata from the image line of the other surface of the document taken bythe second image sensor.

[0020] Also, in the invention, an image reading apparatus reads theindicia on both the upper surface and the lower surface of the documentstransported by automatic document feeder means for feeding documentsstacked on a document supply tray one sheet at a time. The apparatus iscomposed of transport rollers for transporting documents from thedocument supply tray toward a reading position, first light source meanscomprising a xenon lamp to illuminate one surface at the readingposition of the document transported by the transport rollers, a firstimage sensor for reading the light reflected from the documentilluminated by the first light source means, second light source meanscomprising an LED (light emitting diode) disposed downstream of thefirst reading position in the document transfer direction transported bythe transport rollers, to illuminate the other surface of the documenttransported at a second reading position, a second image sensor to readthe light reflected from the document illuminated by the second lightsource means and a white plate to shield light from the first lightsource arranged opposite to the second image sensor. These togetherprevent interferences of the lights from the first light source and thesecond light source, and because a white plate is arranged, theapparatus is capable of reading the image data properly even from a thindocument.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a longitudinal sectional view of the entire structure ofan image reading apparatus according to the first embodiment of theinvention.

[0022]FIG. 2 is a partly enlarged sectional view of essential members ofthe embodiment shown in FIG. 1.

[0023]FIG. 3 is a sectional view taken along line 3-3 of FIG. 2.

[0024]FIG. 4 is perspective view showing an upper unit of the imagereading apparatus according to the first embodiment of the inventionshown in FIG. 1 in an upwardly opened state.

[0025]FIG. 5 shows a relationship of the arrangement of mechanicalelements of the image reading apparatus.

[0026]FIG. 6 is a flashing control sequence of a first light source ands second light source.

[0027]FIG. 7 is a flashing control sequence and a quantity of a lightsuppressing control sequence of the first light source and the secondlight source.

[0028]FIG. 8 is an example of a control configuration block in an ADF onthis apparatus.

[0029]FIG. 9 is an example of the control configuration block to offsetan L amount in the ADF on this apparatus.

[0030]FIG. 10 is an example of the L amount offset control circuitconfiguration.

[0031]FIG. 11 is an example of the operation flowchart for the L amountoffset along with FIG. 12.

[0032]FIG. 12 is an example of the operation flowchart for the L amountoffset along with FIG. 11.

[0033]FIG. 13 is a sequence to explain the L amount offset control.

[0034]FIG. 14 shows a relationship of a document detection sensor and areading position to explain the L amount offset control.

[0035]FIG. 15 is an example of the prior art.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

[0036] The following is a detailed explanation of the preferredembodiment of the present invention based on the figures provided. FIG.1 is a longitudinal sectional view of the entire structure of the imagereading apparatus relating to the invention. FIG. 2 is a partly enlargedsectional view of the essential members of FIG. 1. FIG. 3 is a sectionalview taken along line 3-3 of FIG. 2. FIG. 4 is a perspective view fromthe upper part of FIG. 1 showing the upper unit of the image readingapparatus according to this embodiment with the top open upwardly.

[0037] In FIGS. 1 to 4, the upper unit 2 is mounted via hinges 33 to themain unit 1 to open upwardly. The outer side of the unit 1 is formed bya frame 3, and a discharge tray 4 is fastened to one side of the frame3. Also, on the upper side of the frame on the opposite side of thedischarge tray 4, there is incorporated a platen 5 (third platen) whichis a transparent glass plate for placing a thick original for readingwhen the upper unit 2 in FIG. 1 is opened in the upper direction.

[0038] Also, on the opposite side of the platen 5 relative to thefastening unit 3 b which is a part of the frame 3 to fasten the platen5, a platen 6 (first platen) which is a transparent glass plate tosupport documents or sheets for reading the images fed one by one, and aplaten 7 (second platen) which is formed of a non-transparent whitematerial to support the documents for reading the images one by onesimilarly, are incorporated in one unit. The fastening unit 3 b fastensthe platen 6 to a step notched on the edge of the platen 6. The platen 6and platen 7 are substantially the same shape and their thicknesses areformed to be exactly the same.

[0039] Furthermore, on the upper surface of the frame 3, a fasteningunit 3 a is formed to fasten the platen 7 in the same way as in thefastening unit 3 b. One edge of the platen 7 is formed with a notch ofequivalent thickness as that of the platen 6 which abuts against theplaten 6 for fastening. In this way, the edges of the platens 6 and 7are both supported by the fastening units 3 a and 3 b, and the otheredges are respectively fastened to other edges and their upper surfacesare fastened to the frame 3 to form a single flat surface.

[0040] A pair of discharge rollers 8 and 32 is located on the end of thedischarge tray 4 to discharge the documents. The discharge roller 8 isdriven by a motor that is not shown in the drawings.

[0041] The frame 3 internally stores a reduction optical system imagesensor to convert the read image data into electrical signals. Numerals9 and 10 are carriages that form a part of the reduction optical systemimage sensor and interlocked to maintain a prescribed distancerelationship while being driven by a motor (not shown in the drawings).In other words, the carriage 10 moves inside the frame 3 in the left andright directions of the drawing.

[0042] On the carriage 9 in FIG. 1 either in a fixed position or amoving situation, there is formed a light source 11 for producing lightto illuminate the document and a reflecting mirror 12 for receivinglight reflected from the document illuminated by the light source 11 andconverting the direction to a horizontal direction reflected light.

[0043] On the carriage 10 in FIG. 2, there are mounted a reflectivemirror 13 to convert the horizontal direction reflected light reflectedfrom the reflective mirror 12 to a vertical direction light beam and areflective mirror 14 that converts the direction of the reflected lightreflected by the reflective mirror 13 to a horizontal directionreflected light in a direction opposite to that of the light reflectedfrom the reflective mirror 12. Numeral 15 is a lens for focusing lightreceived from the reflective mirror 14. The carriages 9 and 10, lightsource 11, reflective mirrors 12 to 14 and light condensing lens 15 forma reduction optical system image sensor. Numeral 16 is an image sensorcomprising a CCD that receives reflected light focused by the lightcondensing lens 15 and converts that into electrical signals. An outputend of an image sensor unit 16 is connected to a lead wire, not shown inthe drawings. Through this lead wire, the image signals of lightreflected from the document are converted and transmitted as electricalsignals into an electrical device, such as a facsimile device, in a copymachine unit which is not shown in the drawings.

[0044] The outside of the upper unit 2 is formed by a frame 17 and anupper lid 20. A pressure member 18 having resiliency to lightly pressand hold a document placed on the platen 5 is fastened on the main unit1 below the frame 17. The pressure member 18 is formed of a layer with aplurality of holes, such as a sponge, having a thickness that allowsresilient deformation and a soft surface layer covering the layer with aplurality of holes from the bottom surface.

[0045] Numeral 17 a is a document reception tray for stacking thedocuments to be fed one by one with indicia thereof to be read. Thedocument reception tray 17 a is formed low at the side of the platen 6to allow the documents to move to the platen 6. At the documentreception tray 17 a near the platen, there are formed a pair of paperfeed rollers 19 and 22 that pinch the document to supply to the platen 6one by one stacked on the document reception tray 17 a. A part of theframe 17 on the right side of the feed roller 19 forms the flat portion17 b. Between this flat portion 17 b and the upper lid 20 which storesthe contact image sensor and is described later, an entrance 20 isformed to receive the documents to transport them one by one to theimage sensor. A pair of transport rollers 40 and 23 is formed in thesame way as the feed rollers 19 and 22 between the entrance 21 andplaten 6 to transport the documents inserted from the entrance 21 to theplatens 6 and 7. Also, from the feed rollers 19 and 22 up to theaforementioned discharge roller 8, a document transport path 24 isformed to pass through the upper and lower plate members 45 and 46including a flat portion 17 c. The discharge rollers 19 and 40 aredriven by a motor that is not shown in the drawings.

[0046] Furthermore, numeral 48 is an upper guide for introducing thedocuments from the document reception tray 17 a to the transport path 24and a stopper to stop introduction of the documents which operatesaccording to the timing of reading and paper feeding.

[0047] A light source 25 to illuminate the images on the other surface(surface facing upward) of the document transported into the transportpath 24, a protective glass 27 to pass the illuminating light and lightreflected from the other surface of the document, a Selfoc lens 26 tomake the reflected light parallel, an image sensor unit 28 for detectingthe light passing through the Selfoc lens and for converting it intoelectrical signals, a circuit board 30, are fixed as a single unit toform a compact image sensor (hereinafter referred to CIS).

[0048] A plate-shaped backup guide 39 is fastened at the edge of amember 39 a in the direction of transport to the CIS forming the CISunit 29. The backup guide 39 is supported by a pair of rotation pins 31(FIG. 3) that protrude from left and right side plates 42 on the upperlid 20, and the CIS unit 29 rotates around the rotation pins 31 as thefulcrum. Also, one end of each of a pair of pressure springs 34 to pressdownward the CIS unit 29 is attached to the transport path reardirection portion 39 b in the backup guide 39 (FIG. 3), and the otherend thereof is attached to each of spring support members 49 whichprotrude to the side from the upper sides of the left and right sideplates 42. As shown in FIG. 2, at the lower portion of the dischargerollers 8 and 32, spacers 35 are formed on the right and left corners ofthe CIS unit 29. These adjust a gap between the bottom surface of theCIS unit 29 extending to the back-up guide 39 and the protective glass27, and the transport path 24 between the platens 6 and 7, so that thegap becomes suitable for receiving the light image focused on each ofthe image sensors.

[0049] In the image reading apparatus, sensors, such as documentdetection sensors are formed to detect the document transported one byone from the document supply tray, and a control circuit is disposed tocontrol the circuit drive operation of the transport motor (not shown)based on the sensors' detection signals, the movement of the carriages 9and 10, the flashing of the light sources 11 and 25, and the startingand stopping of image data intake from the image sensors 16 and 28.

[0050] The following explains the image reading apparatus relating tothis invention and how images are read.

[0051]FIG. 5 shows a relationship of the arrangement of the mechanicalelements of the image reading apparatus. The documents fed one by onefrom the document reception tray are transported to the image readingstation for the indicia on both surfaces thereof to be read. In thisapparatus, transport of the documents is performed by a stepping motor(not shown) and the travel of the documents is accurately controlled bythe pulse count inputted to the stepping motor.

[0052] As shown in FIG. 5, at the entrance of the image reading station,there is arranged a document detection sensor So to detect the documentthat has been transported thereto. Also, at the distance L1 spaced fromthe document detection sensor So, the first image sensor for readingindicia on one surface of the document (lower surface) is disposed, andat the distance L2 spaced from the document detection sensor So, thesecond image sensor for reading indicia on the other surface of thedocument (upper surface) is disposed.

[0053] The structures of the first image sensor and the second imagesensor are explained in FIG. 1 and FIG. 2, each being equipped with thefirst light source 11 and the second light source 25 for illuminatingthe appropriate surfaces of the document. The light source 25 uses anLED here to lighten the weight of the second image sensor. There arealso 2 rows arranged on both sides of the reading line to achieve abalance with the light amount from the first light source 11.

[0054] Here, if the gap between the first image sensor and the secondimage sensor is made smaller, the apparatus is made more compact.However, the radiating lights from the first light source 11 and thesecond light source 25 will pass through the document to interfere witheach other thereby increasing the danger of noise applied to the imagereading data. On the other hand, increasing the distance for the gapbetween the first image sensor and the second image sensor will reducethe danger of the light interference from the light sources, but can notmake the apparatus more compact. In this apparatus, the distance for thegap between the first image sensor and the second image sensor is madesmall while eliminating the mal-effects of the mutual interference ofthe aforementioned lights.

[0055] For that reason, on this apparatus, as shown in FIG. 5, thetransport path of the documents from the document detection sensor So tothe first image sensor and the second image sensor is shortened aslittle as possible, and by making it in a direct straight line, theapparatus is made more compact while allowing the smooth travel of thedocuments and the fine reading of the image data.

[0056] Also, a white light shield to shield the light from theaforementioned first light source is arranged opposite to the secondimage sensor. These together prevent the interference of the lights fromthe first light source and the second light source, and because thewhite plate is arranged, it provides an apparatus that is capable ofquality reading of the image data even from a thin document.

[0057] Next, referring to FIGS. 5 to 7, explanation is made for themethod in this invention to reduce the mutual interference of lightsfrom the light sources of the first image sensor and the second imagesensor, which are disposed adjacent to each other.

[0058] The control apparatus of this invention starts the counter at thepoint that the leading edge of the document transported to the imagereading station have passed the document detection sensor S0 positionP1.

[0059] As described above, the travel of the document is accuratelycontrolled by the pulse count charged to the stepping motor, thus thecontrol apparatus can accurately detect the time required for theleading edge of the document to reach from the document detection sensorS0 to the reading position of the first image sensor to read the bottomsurface of the document. In other words, the control apparatus startscounting of the pulses charged to the stepping motor for the prescribedtime after the document detection sensor detects the leading edge of thedocument. Then, because the distance of the gap between the documentdetection sensor and the first image sensor reading position is fixed asL1, at the point the count reaches a prescribed value, the leading edgeof the document has reached the first image sensor reading position. Inthe same way, because the distance of the gap from the documentdetection sensor So to the reading position of the second image sensorto read the upper surface of the document is also fixed as L2, the timerequired to reach the reading position of the second image sensor afterthe leading edge of the document sheet passes the document detectionsensor So is also fixed.

[0060] Through this, when the aforementioned document detection sensordetects the leading edge of the document, the apparatus' control meanscontrols the first image sensor and the second image sensor to startobtaining the image data from both of the surfaces of the document aftera predetermined amount of time has passed (just before the leading edgeof the sheet has reached each of the reading positions).

[0061] Also, after the trailing edge of the document has passed thedocument detection sensor So, a timing to pass each of the readingpositions of the first image sensor and the second image sensor is knownin advance. Therefore, after the aforementioned document detectionsensor detects the trailing edge of the document and after passingpredetermined amounts of time, it controls to stop the taking of imagedata from both surfaces of the document from the first image sensor andthe second image sensor.

[0062] The document transport path leading from the document detectionsensor So to the first image sensor and the second image sensor in thisinvention is short and is configured in a straight line throughout thetravel of the document smoothly without slippage, so it is possible toobtain accurate timing for the starting and stopping in taking the imagedata from the first image sensor and the second image sensor inreference to the document detection sensor So position.

[0063] Next, to reduce as little as possible the mutual interferencescaused by the light sources of both the first image sensor and thesecond image sensor that are formed close to each other in thisinvention, the first light source 11 included in the first image sensorand the light source 25 included in the second image sensor arecontrolled to light just before starting the image data reading fromeach of the surfaces of the document and to extinguish just after thestopping of reading of the image data. This completely eliminates theaforementioned mutual interferences caused by the two light sources of11 and 25, excluding when the sheet is passing over a specific range(space from L1 to L2 in FIG. 5).

[0064]FIG. 6 is a timing chart to explain the control of the flashing ofthe light sources. In FIG. 6, after the document passes the settingposition Po of the document detection sensor So, the light source 11lights just prior to the reading position P1 for the first image sensorand the taking or reading of the image data starts. Next, after theleading edge of the document passes the predetermined position P2 thathas been pre-set, the light source 25 for the second image sensor lightsjust before the document reaches the reading position for the secondimage sensor. Then, the trailing edge of the document passes thedocument detection sensor So and after passing the reading position ofthe first image sensor, the light source 9 is extinguished, i.e. theimage reading has been completed. In the same way, the light source 25for the second image sensor is extinguished when the trailing edge ofthe document passes the document detection sensor So and passes thereading position for the second image sensor, i.e. the image reading hasbeen completed. Numerals P0 to P3 indicate the time relating to theleading edge of the document and P4 to P7 indicate the time relating tothe trailing edge of the document.

[0065] When the next document is transported, it repeats in the sameway, and the first image sensor and the second image sensor arecontrolled to light prior to starting the taking or reading of imagedata from both surfaces of the document and to extinguish after stoppingthe reading of the image data. This control of the lighting andextinguishing of the light sources is used effectively in the timing forshielding the light by the document. For example, when the document istransported between the P2 and P3, as the timing to light the secondlight source 25, the shielding of that light for the first image sensorby the document is selected.

[0066] Through this kind of control, only one light source is lit wheneither the leading edge or the trailing edge of the document is at aposition in a prescribed range so that the mutual interferences of thetwo light sources of 11 and 25 are eliminated. However, while both ofthe two light sources of 11 and 25 are lit simultaneously, they mutuallyinterfere with each other. So, the control means of the presentinvention enables a control to suppress the quantity of light from eachof the first light source 11 and the second light source 25 while boththe first image sensor and the second image sensor are taking the imagedata from the document sheet.

[0067]FIG. 7 shows an example of the timing chart to explain theembodiment for suppressing the quantity of light while controlling theflashing of the two light sources explained in FIG. 6. The differencefrom the timing chart of FIG. 6 is that the first light source 11 andthe second light source 25 are lit at the rated brightness when one ofeither the first image sensor or the second image sensor is litindependently, and when both light sources are lit simultaneously, inother words, when taking the data from both the front and the lowersurfaces of the document, the quantities of lights irradiating from thetwo light sources are suppressed. Thus, the image reading apparatus ofthe present invention enables the reduction of the mal-effect caused bythe mutual interferences of the lights of the two light sources arrangedopposite to and close to each other, even if the document is thin. Inthe embodiment of the present invention, the second light source 25 iselectrically controlled to adjust the quantity of light because itemploys an LED. The first light source 11 is a xenon lamp and because itis not lit by an inverter, the average current is controlled bycontrolling the duty of the electric power output.

[0068] When controlling the quantities of lights of the two lightsources in this way, it is good to adjust by the control means thebalance of the intensity of the image data on the bottom surfacedetected by the first image sensor and the image data on the uppersurface detected by the second image sensor. Several methods to adjustthe intensity of the image data from the front and lower surfaces arewell known and will not be described in detail here, but one example isto form a sensor to measure the transparency ratio of light from thedocument and revise gamma table offset processing data for both thefront and lower surfaces based on this analog output value and tobalance the intensity of both the front and lower surfaces.

[0069]FIG. 8 and FIG. 9 show an example of the control configurationblock of this apparatus. FIG. 8 is a control configuration block in theADF on this apparatus of one embodiment of the present invention. As isshown in the drawing, the stepping motor, sensors and image sensors inthe ADF are connected to external devices via an I/O connector shown inthe figures, the external devices performing various controls. Here, thesecond image sensor comprises a CIS line sensor, analog-digitalconversion circuit (A/D), signal shading offset circuit (S/C), LED and aprescribed interface circuit (LVDS: Low Voltage Differential Signaling)arranged and configured on a printed circuit board.

[0070] The quantity of light from the LED is control via the I/Oconnector. In the embodiment of the present invention, it is possible toadjust the quantity of light to 8 levels using a 3 bit control wire asshown in the figure.

[0071] In this invention, two image sensors are used to substantiallysimultaneously take the image data from both the front and lowersurfaces of the document, so it is preferred to offset the difference ofthe image data positions of the two by the amount of L.

[0072]FIG. 9 is an example of the control configuration block diagram tooffset the L amount in the ADF. In FIG. 9, signals from the externaldevices and sensors are received to control the adjustment of thequantity of light for the CIS, which is the second image sensor, and tocontrol the stepping motor circuits on one programmable CPU (PROM).Here, the aforementioned PROM is connected to a memory and stores thedata for offsetting L amount.

[0073]FIG. 10 is an example of the L amount offset circuit. In thecircuit example, there is equipped a memory for the upper surface totemporarily store image data from the upper surface of the document readby the CIS, which is the second image sensor, and it offsets thediscrepancy of the position with regard to the image data on the bottomsurface of the document read by the first image sensor and is capable ofalternately output the image data of both surfaces of the document to anexternal apparatus.

[0074]FIG. 11 and FIG. 12 are examples of an operational flowchart tothe offset L using the circuit shown in FIG. 10. In the explanation ofFIG. 11 and FIG. 12, the positional relationships of the documentdetection sensor (document sensor) So accords to FIG. 14, and thereading position for the bottom surface of the document and the readingposition for the upper surface of the document are made by the timingsequence for reading the images on both surfaces according to FIG. 13.

[0075] The position where the document detection sensor So is formed andthe distance to the position to read the bottom surface of the documentby the first image sensor is equivalent to the image line count A to beread. Also, the position where the document detection sensor So isformed and the distance to the position to read the upper surface of thedocument by the second image sensor is equivalent to the image linecount B to be read. Therefore, the first image sensor and second imagesensor can start reading the image data of both surfaces of the documentafter the leading edge of the document is detected and after thecorresponding pulse counts A and B are counted. However, because thereis the possibility of the document skewing in the transport path, G2 andG1 are set for the maximum values for the corresponding skew, so thatthe reading of the image data starts early in consideration of that.

[0076] As shown in FIG. 13 and FIG. 14, the reading of the image data onthe bottom surface of the document starts by the rise of the signal LWRand takes the image data by synchronizing to the bottom surface clocksignal prescribing the timing for reading the bottom surface.Furthermore, the reading of the image data on the upper surface of thedocument sheet starts with fall of the signal UPR and takes the imagedata by synchronizing to the upper surface clock signal.

[0077] In the operational flowchart of FIG. 11 and FIG. 12, each counteris set to its initial value (S11 and S12), and when the documentdetection sensor So detects the leading edge of the document, thecounters CN1 and CN2 are respectively set to the numerical values A andB (S14). The numerical values A and B, as explained in FIG. 14, arevalues calculated into the line of the image (CLK) to read the distancebetween the set position of the document detection sensor So and theposition for reading the bottom of the document by the first imagesensor, and the distance between the set position of the documentdetection sensor So and the position for reading the top of the documentby the second image sensor.

[0078] First, the top of the image data on the bottom surface of thedocument is set. Here, when the line to read is moved, the counters CN1and CN2 decrement (S15 and S16). Then, when the counter CN1 reaches 0,the bottom surface reading signal LWR becomes active (S18) and readingof the bottom surface of the document starts with the first imagesensor.

[0079] Next, the L offset for the image data on the bottom surface ofthe document sheet is performed. When the line to read is moved, thecounter CN2 decrements (S20). Then, when the counter CN2 reaches 0(S21), the upper surface reading signal UPR becomes active (S22) andreading of the upper surface of the document starts with the secondimage sensor. Here, the image data remaining on the bottom surface ofthe document is output and the image data for the upper surface of thedocument sheet is saved to the memory. Then, the numerical value S1 isset to the counter CNT (S23), and each time the line to read moves, thecounter CNT decrements (S25). When it reaches 0 (S26), it switches tooutput the image data of the upper surface.

[0080] Next, S1 is set to the counter CNT (S28) and the address counteris reset (S29). Each time the line to read moves (S30), the counter CNTdecrements (S31). When this reaches 0, the upper surface image datasaved in memory is sequentially read.

[0081] As described in detail above, this invention controls to startthe reading of the image data on both of the surfaces of the document bythe first image sensor and the second image sensor after prescribedamount of time has passed since the leading edge of the document hasbeen detected and to stop the reading of the image data on both surfacesof the document by the first image sensor and the second image sensorafter a prescribed amount of time has passed since the trailing edge ofthe document has been detected.

[0082] Also, because the invention is configured to alternately outputthe image data of the line that was read on one surface of the documentread by the first image sensor and the image data of the line that wasread on the other surface of the document read by the second imagesensor, high speed image processing efficiency is made.

[0083] Thus, in the image reading apparatus relating to this invention,the need to arrange a plurality of document detection sensors on aplaten comprising two reading stations for reading the front and lowersurfaces of a document sheet is eliminated while simplifying the timingcontrol to start the reading of the image data. The first light sourcefor the first image sensor and the second light source for the secondimage sensor are controlled to light just prior to the start of readingthe image data for that particular surfaces of the document and arecontrolled to extinguish immediately after the stopping of the readingimage data. Furthermore, while taking the image data from the surfacesof the document by the first image sensor and the second image sensor,the first light source and the second light source are controlled tosuppress the quantity of lights from the light sources therebyminimizing the mutual interferences of lights irradiated from the twovertically opposing light sources to thereby effectively reduce thenoise that occurs in the image data read from the surfaces of thedocument. Also, by controlling the lighting and extinguishing bygrasping the positions of the image sensors to effectively use thedocument to shield light, the invention is further improved.

[0084] Also, a white light shield to shield the light from the firstlight source is arranged opposite to the second image sensor. Thesetogether prevent interferences of the lights from the first light sourceand the second light source, and because the white plate is arranged, itprovides the apparatus that is capable of reading the image data evenfrom a thin document.

[0085] While the invention has been explained with reference to thespecific embodiment of the invention, the explanation is illustrativeand the invention is limited only by the appended claims.

What is claimed is:
 1. An image reading apparatus for reading images ontwo surfaces of a document transferred by an automatic document feederone by one, comprising: a document detection sensor for detecting thedocument transported by the automatic document feeder; a first imagesensor to read an image on one surface of the document; a second imagesensor to read an image on the other surface of the document; and acontrol device connected to the first and second image sensors and thedocument detection sensor, said control device starting to take imagedata from the first image sensor and the second image sensor at pointswhere prescribed amounts of time for the respective sensors have passedafter the document detection sensor detects a leading edge of thedocument.
 2. An image reading apparatus according to claim 1, whereinsaid control means has counter means for counting time after thedocument detection sensor detects the leading edge of the document, andmemory means for storing the image data, starts to store the image datafrom the first image sensor to the memory means when a counter value ofthe counter means reaches a predetermined first counter number, andstarts to take effective image data from the second image sensor when acounter value of the counter means reaches a predetermined secondcounter number different from the first counter number.
 3. An imagereading apparatus according to claim 1, further comprising control meansfor A/D conversion of the image data read by the first image sensor andthe second image sensor and equipped with recording means to temporarilystore converted data, wherein reading of both surfaces of the documentis configured to alternately output the image data of a line on onesurface of the document read by the first image sensor and the imagedata of a line on the other surface of the document read by the secondimage sensor.
 4. An image reading apparatus according to claim 1,wherein said first image sensor is composed of an optical reductionreading sensor, and said second image sensor is composed of a contactimage sensor.
 5. An image reading apparatus according to claim 3,wherein said control means offsets a positional difference in a transferdirection of the document of the first image sensor and the second imagesensor in outputting the image data from both two surfaces of thedocument.
 6. An image reading apparatus according to claim 5, whereinoffset of the positional differences is performed by controlling atiming to start storing in the recording means image data read by thefirst image sensor and the second image sensor.
 7. An image readingapparatus for reading images on two surfaces of a document transferredby an automatic document feeder one by one, comprising: a documentdetection sensor for detecting the document transferred by the automaticdocument feeder; a first image sensor to read an image on one surface ofthe document; a second image sensor to read an image on the othersurface of the document; and a control device connected to the first andsecond image sensors and the document detection sensor, said controldevice stopping to take image data from the first image sensor and thesecond image sensor until predetermined amounts of time have passed forthe respective image sensors after detection of the trailing edge of thedocument by the document detection sensor.
 8. An image reading apparatusaccording to claim 7, wherein said first image sensor includes a firstlight source, and the second image sensor includes a second lightsource, said light sources being controlled to light prior to starttaking image data from the surfaces of the document and to extinguishafter stopping to take the image data.
 9. An image reading apparatusaccording to claim 8, wherein at least one of said first light sourceand said second light source is controlled to suppress a quantity oflight thereof while simultaneously taking the image data from the firstimage sensor and the second image sensor.
 10. An image reading apparatusaccording to claim 7, wherein said first image sensor is composed of anoptical reduction reading sensor, and said second image sensor iscomposed of a contact image sensor.
 11. An image reading apparatusaccording to claim 7, further comprising a substantially straighttransport path between said first image sensor and said second imagesensor to transfer the document.
 12. An image reading method for readingimages on two surfaces of a transferred document comprising the stepsof: detecting said transferred document by a document detection sensor,starting to read image data on one surface of said document from a firstimage sensor when a predetermined amount of time has passed after thedocument detection sensor detects a leading edge of the document, andstarting to read image data on the other surface of the document from asecond image sensor when a predetermined amount of time has passed aftersaid document detection sensor detects the leading edge of saiddocument.
 13. An image reading method for reading images on two surfacesof a transferred document comprising the steps of: detecting thetransferred document by a document detection sensor, starting to readimage data on one surface of the document from a first image sensorafter a first predetermined amount of time has passed since the documentdetection sensor detects a leading edge of the document, starting toread image data on the other surface of the document from a second imagesensor after a second predetermined amount of time has passed since thedocument detection sensor detects the leading edge of the document,stopping to read the image data on the one surface of the document fromthe first image sensor when a third predetermined amount of time haspassed after the document detection sensor detects a trailing edge ofthe document, and stopping to read the image data on the other surfaceof the document from the second image sensor when a fourth predeterminedamount of time has passed after said document detection sensor detectsthe trailing edge of the document.
 14. An image reading method accordingto claim 13, further comprising controlling a first light source for thefirst image sensor and a second light source for the second image sensorto light just prior to start to take the image data from both surfacesof the document and to extinguish after stopping to take the image data.15. An image reading method according to claim 14, wherein quantities oflights from the first light source and the second light source aresuppressed when simultaneously taking the image data from the firstimage sensor and the second image sensor.
 16. An image reading apparatusfor reading images on two surfaces of a document transferred by anautomatic document feeder one by one, comprising: transport rollers totransfer a document one by one; first light source means forilluminating light on one surface of a document transferred by thetransport rollers at a first reading station; a first image sensor toread light reflected from the document illuminated by the first lightsource means; second light source means for illuminating light on theother surface of the document transferred by the transport rollers at asecond reading station located downstream of the first reading stationin a transfer direction of the document; a second image sensor to readlight reflected from the document illuminated by the second light sourcemeans; and a white light shield to shield the light from the first lightsource arranged opposite to the second image sensor.
 17. An imagereading apparatus according to claim 16, wherein said first light sourcemeans and said first image sensor are located in a light path of anoptical reduction system having a reflective mirror, and said secondlight source means and said second image sensor are located in a lightpath of a contact image sensor.
 18. An image reading apparatus accordingto claim 17, wherein said first light source means is comprised of axenon lamp and said second light source means is comprised of a lightemitting diode.